SEOUL, Aug. 6 (Yonhap) -- The number of North Koreans who visited the United States in the first half of the year jumped by more than 50 percent on-year, a U.S. report claimed Saturday.

Radio Free Asia (RFA), citing data from the Department of Homeland Security, said 139 North Korean nationals entered the country during a six month period in 2010, up from 89 tallied in the same period the previous year.

It said that despite the drop in official contacts between Washington and Pyongyang, and a general cooling off in bilateral relations, there was a rise in the inflow of North Korean nationals into the country.

Two-way contacts have been adversely affected after the communist regime bolted from the six-way talks aimed at ending North Korea's nuclear ambitions. The sinking of a South Korean warship near the inter-Korean sea border and the shelling of a civilian island in the Yellow Sea by North Korean artillery last year further strained relations.

The RFA said a delegation of North Korean scientists visited in February, followed by an economic delegation the following month and 17 martial arts experts in June that toured three east coast states.

The radio station said the U.S. State Department mainly issued short term, non-immigration, commercial B1 or B2 tourism visas to the North Korean visitors.